Process and apparatus for heat transfer with granular solids



PROCESS AND APPARATUS FOR HEAT TRANSFER WITH GRANULAR SOLID Filed Aug. v2, 1946 July 13,1948.- A y E. uTTERBAcK y y 2,445,092

HOPPER ERNES UTTERBHCK Patented July 13, r1948 PROCESS AND APPARATUS FOR HEAT TRANSFER WITH GBANULAB SOLIDS Ernest Utterback, New York, N..Y., assignor to Sunny-Vacuum Oil Company, Incorporated, a corporation of New York Application Auml z, 194s, serial No. 087,901

l 17 Claims.

and efllciently raising the temperature of the granular solid heat transfer agent. Inone specific embodiment the invention contemplates transfer of heat from the novel heater of this invention to a reactor by means of a granular solid and contacting a hydrocarbon charge with the granular solid in the reactor to crack the charge under carefully controlled conditions of temperature and reaction time. According to this preferred embodiment of th'invention. a portion of the hydrocarbon charge is derived from the heater. s

For many purposes, transfer of heat by means of a granular solid has been found to be extremely effective. Thus, contact with a granular vsolid atkelevated temperature may be used effectively to vaporize liquids and solids and to induce high temperature reactions where the rate of heating, average temperature, maximum temperature and residence time at elevated temperature are important factors. The process is found particularly advantageous where the conversion. either in physical state or chemical constitution. may result in fouling of metallic heat transfer surfaces vsuch as tubes and shell stills.

An exemplary process is the conversion of high boiling hydrocarbons to low molecular weight olens such as ethylene and, acetylene by reaction at high temperature for short reaction periods, Thus, gas oils, propane and ethane may be converted at temperatures on the order of 1350 to 1800 F. to high yields of ethylene. The reaction time varies inversely with the temperature and,4 in general, higher temperatures are required for lower molecular weight hydrocarbons. Yields on the order of 30% by weight of ethylene may be obtained by cracking gas oils at 1450 F. for 0.2 second. This process of cracking hydrocarbons is disclosed herein as exemplary `for purposes of illustration and is not to be taken as limiting of the invention.

In a preferred embodiment, a portion of the hydrocarbon charge for a cracking process'is derived froma preparatory stage of the heater and, in this aspect, the invention is directed to hydrocarbon cracking.

It has been found that a number of diillculties are encountered in attempting to attain maximum eillciency and minimum maintenance costs in a heater for the purposes described above.

Pre-mix burners must be carefully controlled as to number and operation in order to limit flame temperatures to those which will not induce fu-` sion of the granular solid in the immediate vicinity of the burner. On the other hand. the combustion vmust be so conducted as to obtain reasonably complete conversion of carbonto carbon dioxide within the actual heating zone since resldualamounts of carbon monoxide in excess of the equilibrium quantities will result in combustion of the carbon monoxide in ilues, waste heat boilers and the like to give undulyl high temperatures in portions of the apparatus not designed for handling elevated temperatures. This afterburningtmay result in burning out o f ilues and 1'5 tubes of waste heat boilers.

According to the present invention, highly eilicient heating of the granular solid is obtained by coating the granules or eiiiciently mixing the same with a fuel which is thereafter burned by air in direct contact'with the granules in a .cam-

pact downwardly moving bed. By this means, combustion takes place uniformly throughout the compact bed of particles and temperatures can readily be controlled to be maintained below fusion ltemperature of the solid and above the ignition point of carbon monoxide.

Flow of combustion air through the compact bed may be either concurrent or countercurrent. Each type of ilow has advantages peculiar to it and the characteristics o! combustion should be examined in connection with the particular problems involved to design a heater for best flaw in any desired use. Under conditions of counter-current ow, the air is rst brought into contact with small residual amounts of fuel in the presenceof granules at high temperature ,and combustion of the residual fuel readily takes place. As the air passes upwardly through the bed it contacts progressively greater amounts of more readily burned fuelv and llame temperatures are minimized because the regions of high fuel concentrationare regions of low oxygen'concentration. Addition.- ally, the flue gases from 'countercurrent llow are at about the same temperature as the incoming solid, thus making more effective use of the in the heater and leaving less residual heat to be recovered in waste heat boilers and the like.

On the other hand. concurrent now offair results in flue gases of maximum temperature thusy minimizing the chance of large residual amounts of carbon monoxide which may burn in nues and the like to produce disadvantageous results and low levels of economic operation. These andother objects and advantages ofthe invention are y brought out by reference to a specic process adapted to be practiced in apparatus shown in the annexed drawings; wherein Figure 1 is a generally diagrammatic view of the apparatus for the `cracking of hydrocarbons, showing the heater in vertical section; and

Figure 2 is a detail view showing a preferred construction of collection or distributer elements for the bottom of the heater.

Gas oil is readily cracked to high yields of ethylene by passing the charge in liquid phase to the bottom of a downwardly moving compact bed of granular solids in a reactor Il. The liquid charge is admitted'by line il and vaporized by contact with hot granular solid, the vapors passing upwardly through progressively hotter granules to be rapidly cracked `and the cracked product is removed at discharge line I2 and rapidly quenched to a temperature at which the cracking reaction is substantially inhibited. Granular solid at a temperature of about 1575 F. is admitted to the top of reactor Il from feed leg i3 and is cooled to about 900 F. by passing through the reactor. Granular solid at this temperature is discharged through conduit il having a valve Il to an elevator I8. The granular solid from the top ofelevator Il is transferred toconduit Il to a supply hopper Il from which the granular solid passes downwardly through feed leg il hav- A ing a steam sealing zone 2t and a valve 2l to a heater 22.

'Ihe granular solid entering the top of heater 22 is deflected toward the walls of heater 22 to .give a shower of free falling discrete particles As shown, thisresult -f may be obtained by dropping :the solid onto a of heat transfer agent.

conical spreader 22. A fuel from pipe 24 is sprayed into the shower of solid granules from 'use of solid fuels, particularly those which can be caused to intumesce and thereby coatthe A granules; for example, many of the readily available coals.

lMany of the fuels adapted to the present purpose are partially volatile at the temperature of the incoming granules and vapors will be evolved from the fuels sprayed into the top of heater 22.` These 'vapors are advantageously withdrawn at discharge port 2t and transferred by line 21 to be mixed with the charge `for reactor Il, as shown in Figure 1. If it is desired to insure that all the charge enters reactor Il as liquid, the vapors from port 2t may be `condensed by inserting a suitable heat exchanger in line 21. Alternatively, charge may be introduced through line Il in vapor phase by vaporizing a gas oil in a suitable tube still and mixing therewith vapors from line 21.

The granular solid is caused to accumulate in the upper portion of heater 22 as acompact bed of granules coated and/or mixed with fuelfrom Thus, heavy resicapacity of the condenser with change in the nature of the dielectric between the plates.

Granular solid is transferred through a zone of restricted cross section from thev solid bed above plate 2l to the combustion zone therebelow. The restricted cross section of the transfer means has a stronginhibiting effect on gas flow across lthe plate 2l and thus maintains an adequate gas seal` across the plate so long as excessive pressure differentials are avoided. In the embodiment shown, transfer is by means of feed pipes 2l depending from the plate 2l which give f uniform distribution across the top of the bed in the combustion zone and also provide a plenum chamber above the combustion bed. In the case of concurrent flow of preheated combustion air, the latter is admitted by pipe il to the plenum chamber below plate 2l and passes downwardly through'the bed to suitable collecting devices in the lower portion thereof. As i shown in Figure 2, the collecting devices consist of upright pipes '3i `mounted on and passing through a plate 32 and having a plurality of inverted cup shaped member I2. The cups Il receive gases of combustion which pass through orifices 24 in the pipes 2| to be diverted to a plenum chamber below `plate 22 about draw-of! pipes 25. The combustion gases are then by pipe 36 to a waste heat boiler and thence to the stack. Plates 21 and Il below the plate 32 serve to induce uniform rate of flow through the several pipes 25 and thus cause uniform rate of flow throughout the combustion zone. The

spray head 2l. This bed is sustained by plate 2l and a suitable ,upper level is maintained by installing a level responsive element 29 connected with an automatic level control ll which serves to operate valve 2|. Among the devices suitable for level control are reciprocating rods and electrical devices such as condenser plates which indicate the level by detecting changes in the highly heated granular solid,` for example at' 1600* F. is transferred by feed line Il having a steam sealing zone Il to the reactor Il for completion of its cycle.

It will be readily apparent how the same apparatus may be employed for passing combustion air in countercurrent contact with the granular solid in heater 22 by admitting preheated air through pipe 3l and withdrawing products of combustion by pipe Il. This alternative type of operation is illustrated in the drawing by broken line arrows.

I claim: s

1.V A process for cracking hydrocarbons which comprises passing a granular solid heat transfer materialdownwardly through a heating zone as a compact moving bed, passing the heated material downwardly through a cracking zone, passing charge hydrocarbons in direct contact with said material in said cracking zone. dropping heat transfer material cooled by cbntact with said charge as a continuous shower/of yseparate granules through a fuel supply zone, {continuously spraying a khigh boiling liquid hy '/'/W' y fuel into said shower to thereby apply the surface of said granules and vaporize a'f//ortion of said fuel, removing vapors so gener l and adding said vapors to said charge hydrocifbons for direct contact with said heat transfer material in saidcracklng zone, transferring said granular material fromsald fuel supply zone fto said heating zone, and passing air through said bed of granlar solid in said heating zone in concurrent ilow with said downwardly moving bed to burn said fuel and heat said granules 2. A process for cracking hydrocarbons which continuously hy: drocarbon fuel into said shower to thereby apply fuel to thesurfaee of said granules and vaporize hydrocarbons vfor directL contact with said heat transfer material in said cracking zone, transfemm ma granularmanal from said mel supplysonetosaidheatingzone,andair through said .bed of granular solid in said heating zone in countercurrent flow with said downa compact vmoving bed, passing the heated mate-4 rial downwardly throughv a cracking zone. passing charge hydrocarbons in direct contact with said material in said cracking zone, dropping heat transfer material cooled by contact with said charge as a continuous shower of separate granules through. a fuel supply zone, continuously spraying a high boiling liquid hydrocarbon fuel into said shower to thereby apply fuel to the surface of said granules and vaporize a portion of said fuel, removing vapors so generated and adding said vapors to said charge hydrocarbons for direct contact with said heat transfer material in said cracking zone, transferring said granular material from said fuel supply zone to said heating zone, and passing air through said bed of granular solid in said heating zone to burn said fuel and heat said granules.

4.- A process for crackinghydrocarbons which comprises passing a granular solid heat transfer material downwardly through a heating zone as a compact moving bed, passing the heated material downwardly through a cracking zone, passing charge hydrocarbonsin direct contact withsaid material in said cracking zone, dropping heat transfer material cooled by contact with said charge as a continuous shower of separate granules through `a' fuel supply zone, continuouslyspraying a fuel which is predominantly non-volatile at the temperature of granules in said shower into saidz shower to thereby apply fuel to the surface of said granules and vaporize a portion of said fuel, removing vapors so generated and adding said vapors to said chargehydrocarbons for direct contact with said heat transfer material in said cracking zone, transferring said granular material from said fuel supply zone to said heating zone, and passing air through said bed of granular solid in said heating zone to burn said fuel and heat said granules.v

5. A process for cracking hydrocarbons which 6 comprises passing a granulary solid heat transfer materiali downwardly through a heating zone as a compact moving bed, passing the heated materialdownwardly through a'cracking zone, pass-k ing charge hydrocarbons in direct contact with saidv material in said cracking zone, dropping heat-transfer material cooled by contact with said charge as a continuous shower of separate granules'through a fuel supply zone, continuously spraying powdered coal into said shower to thereby apply fuel to the surface -of said'granules and vaporize a portion -of said fuel, removing vapors so generated land adding 'said vapors to said charge hydrocarbons for direct contact with said heat transfer material in said cracking zone,

heat said granules.

8. A process for heating a granular solid heat transfer material which comprises droppin! said material as ya continuous shower of vdiscrete freely-falling granules through a fuel supply zone to a compact bed of' said granules in the lower part of saidv zone, maintaining the top of said.

bed substantially at a predeterminedlevel, con'- tinuously spraying a high boiling liquid fuel into said continuous shower, passing said granular material together with fuel applied thereon by said spray from said bed downwardly through a heating zone as a compact moving bed and passing air in direct contact with said granules in part of said zone. maintaining the top of said bed substantially at a vpredetermined level, continuously spraying a fuel into said continuous shower, passing said granular material together vwith fuel applied thereon by said spray from said bed downwardly through a heating zone as a compact moving bed and' passing air in direct contact with said granules in said last named 3 bed to burn said fuel and thereby heat said granules. l

8. A process for heating a granular solid heat transfer material which comprises dropping said material as a continuous shower of discrete freely-falling granules through a fuel supply zone to a compact bed of said granules in the lower part of said zone, maintaining the top of said bed substantially at a predetermined level, continuously spraying powdered coa'. into said con- 4 tinuous shower, passing said granular material together with fuel applied thereon by said spray from said bed downwardly through a heating zone as la compact moving bed and passing air in direct contact with said granules in said .last named bed to burn said fuel and thereby heat .said granules.

9. A process for heating a granular solid heat transfer material which comprises dropping said material as a continuous shower of discretefrceiy-faliing granules through a fuel supply zone to a compact bed of said granules in the lower part of said zone, maintaining-the top of said bed substantially at a predetermined level, continuously spraying a fuel into said continuous shower, passing said granular material together with fuel applied thereon by said spray from said bed downwardly through a transfer zone of lrestricted cross section to and through a heating zone as avlcompact moving bed and passing air in directA contact with said granules in said last named bed to burn said fuel-and thereby heatr said granules. i

l0. A process for heating a granular solid heat transfer material which comprises ldropping said material as a continuous shower of discrete frecly-faliing granules through a fuel supply rsume to a compact bed of said granules in the lower part of said zone, maintaining the top of said bed substantially at a predetermined level. conu 'Iv m1110981! Slirarina l fuel into said shower, passing said granular material together with fuel appliedthereonby said spray fromsaid beddownwardlythroughaheatinglxoneasa,

compactmovinglbedandpassingairinconcurrent flow contact with said granules insaid last named bed to burn said fueland thereby heat said granules.

1l. A process for heating a granular solid heat transfer material which comprises dropping said material as a continuous shower of discretefreely-falling granules through a fuel supply :one to a compact bed of said granules-in the lower part of said anne, maintaining the top of said bed substantially at a predetermined level, continuously spraying a fuel into said continuous shower, passing said granular material together with fuel applied ythereon by said spray `from said bed downwardly through a heating zone as a compact moving hed andpasslng air incountercurrent `ilow contact with said granules in said last named bed to burn-said `fuel and thereby heat said granules.

12. A heater comprising a `vertical shell, a supply conduit to admit granular solid material to the top of said shell;I a conical spreader in the top of said shell below said conduit, a liquid spray device under said spreader. means to supply liquid to said device, a valve in said conduit, means below said spray device responsive to the level of a compact bed of solid controlling said valve, a plate across said shell below said last named means, a plurality of feed pipes extending downwardly from said plate, llow control means in the bottom of saidshell for removing granular solid therefrom uniformly across said shell. means to admit air below said plate and means tomithdraw gaseous products of combustion from the lowerportionofsaidshell. -m

13. A heater comprising a vertical shell, a su ply conduit to admit granular solid material to thetopofsaidshell; aspreaderinthetopof shell below said conduit to deilect solids from said conduit toward saidsbell, aliquld spray device undersaidspreadeameanstosupplyliquidto said device, a valve in said conduit, means below said spray devlceresponsive to the level of a compact bed of solid controlllngsaid valve, a plate actos said shell lielow said last named means, a plurality of feed pipes extending downwardly fnomsaid plate, ilow control means in the bottom of said shell for removing granular solid therefrom uniformly' across said shell, means to admit airbelowsaid plate and means to withdraw g products of combustion from the. lower portion of said shell.

14. Aheatercomprisingaverticalshenasupply conduit to admit granular solid material to the top of said shell; a conical spreader in the top of said shell below said conduit, a liquid spray device imder said spreader, means to supply liquid to said device. means to maintain a predetermined upper surface of a bed of granular solid in said shell. aplate across said shell below said last named means, a plurality of feed pipes extending downwardly from said plate, llow control means in the `bottom of said shell for removing granular solid therefrom uniformly across said shell, means to admit air below said plate `and means to withdraw gaseous products of combustion from the lower portion of said shell.

15. Alieata'colnll'lllngavertlcalmampplycondldtto admitgrannlaraolldmaterialto uidtosaiddeviavalvemaaidconduihcontrolmeanslielowsaidsptaydevicereaponsiveto thelevelof acompactbedofsoldcontrolling saidvalmcondnitmeansofrestrictcdcmas-scctlmbelolsaidcmtrolmcanameamtodivert solidsthroughsaldcmduitmeamflowcontrol meansinthebottomolsaldahellforrenwvlng granularsolldtherdrmnuniformly across said shelimeanstoadmitalrbelowaaldcmdultmeans andmeamtowithdxawgaseouspmductsofcombastionfromthelowerportionolsaidlhell.

16.Alxcateravcrticalshell,amp plyconduittoadmltgranuhrsolidmaterlalto thetopofsaidsheluslleadermthetopofsaid shell belowsaid conduit todeliect solidsfrom said conduit towardsaid shell, aliquid spray deviceundersaidspreader,meanstosupplyliq uldtosaiddevicacmtmlmeanstomaintaina prupperlevelofabcdofgranular solidinsaid shelbcondult means ofrtricted cros-secticnlntermediatetheendsofsaidshell, means to divert downwardly moving granular solidthrough said cmiduit means, llow control meanslnthebottomofsaidshellforremovins granular solid-therefrom uniformly across said shelLmeanstoadmitalrbelowsaidconduit meansandmeamtowithdrawgaseousproducts ofcombustionnumihelowerporilonofsaid shell.

l'LAheateravertlcalslielLasupplycmduittoadmitgranularsolidmaterlalto the'topofsaidshell; aspreaderinthetopof saidshellbelowsaidcaxduitto decctsolilrom saidconduit'towardsaidshenaliquidspray' deviceundersaidslxeader-,meanstosupplyliquidtosaiddevicecixol'meamtomaintaina predetermincdupperlevelofabedofgranular solidmsaidshelconduitmeansofrestrlcted cross-scctimintermediatethemdsotsaidsheli, means to divert downwardly moving granular sclidthmnghsaldcondultmeanamcanstoadmitairbehwaaldcmdultmeansandmcansto wlthdrawgasemslnnductsofirom thelowerp'tionctsaidshell.

UTIIRBACK.

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